In recent years, with high pixilation of an image pickup device (a CCD), a camera module for use in a portable terminal such as a cellular phone is required to have functions similar to those of a usual electronic camera (a digital camera), such as a high-speed high-precision auto-focus (AF) function and a focal length change (zoom) function. Furthermore, with miniaturization and lightening of the portable terminal itself, it is necessarily demanded that the camera module should be miniaturized and lightened.
In order to perform auto-focusing and changing of a focal length (zooming) in such a camera module, a lens unit needs to be moved in an optical axis direction. To achieve this, in a conventional technology, as described in, for example, Patent Document 1, a cylindrical cam is disposed on a side surface of an optical system. Moreover, a bearing of the cylindrical cam and a bearing of a lens frame are arranged on a front cover (a fixed frame), and driven by a motor, and a zoom lens frame and an AF lens frame are driven. Furthermore, a solid image pickup device (the CCD) is directly disposed in a housing (a case), and a rotation angle of the cylindrical cam is detected by a cam and a mechanical switch which are arranged on the side surface of the cylindrical cam to detect the rotation angle.
Moreover, a stepping motor is provided integrally with a lead screw, and the lead screw is independently held by holding members together with the stepping motor. Attachment members to attach these holding members to a housing which is a lens barrel substrate are arranged on only one side of the lead screw. Here, the zoom and AF lens frames are driven by two lead screws, the housing is provided with guide support portions of the lens frames, and the CCD is disposed in a lower part of the housing.
In addition, a focus motor and a zoom motor for driving photographing lenses and a shutter motor and an aperture stop motor for driving an inner mechanism are arranged. These motors are arranged in first to fourth quadrants obtained by dividing a plane crossing an optical axis of each photographing lens at right angles by first and second axes which cross the optical axis at right angles and which cross each other at right angles, respectively. A base of a shutter unit is provided with cutout portions for passing rotary center axes of the focus motor and the zoom motor.
Moreover, a movable lens is driven in the optical axis direction by a screw shaft, a bearing section which rotatably holds the screw shaft in a main body is integrally formed by molding, and the bearing section is formed by a plurality of slide molds having mutually different slide directions. Here, the zoom and AF lens frames are driven by two lead screws, an upper housing bears two lead screws and two lens frame guide shafts, and a lower housing holds the CCD.
However, in such a conventional camera module using the cylindrical cam, the lead screws, helicoids and the like, an electromagnetic motor and a pulse motor having rotors are generally used as driving sources of the module. However, the electromagnetic motor using such a rotor requires an electromagnet and a permanent magnet for the rotor and around the rotor. Even when a length in an axial direction is reduced, a columnar portion is indispensable. This hampers the miniaturization of the camera module. Furthermore, noises and the like are generated.
Therefore, in order to solve shortcomings of such an electromagnetic motor, as the driving source which moves the lens frames in the optical axis direction, a frictional driving type driving source has heretofore been used in which a mechanical vibrator is constituted of a piezoelectric element such as a piezo element (a PZT) to generate a mechanical strain in accordance with changes of an electric field and a magnetic field. The rotor or a slider is brought into contact with this mechanical vibrator to take out a vibration of the mechanical vibrator as an output. Such a frictional driving type driving source operates at a low speed but has advantages that the source has a high torque and excellent response and controllability, can finely be positioned, has a holding torque (or a holding force) when not energized, has excellent quietness and is small and light.
It is described in, for example, Patent Document 2 that one end of a laminated piezoelectric article is fixed to a protrusion of an outer peripheral surface of a lens holding unit, one end of a bimorph piezoelectric article is fixed to the other end of the piezoelectric article, and another bimorph piezoelectric article is fixed on a side opposite to the protrusion. When a voltage turns on, these bimorph piezoelectric articles are bent to disconnect engagement members on distal ends of the articles clamped to an inner surf ace of a lens barrel. Moreover, when the voltage turns on, a laminated piezoelectric element elongates. When the voltage turns off, the bimorph piezoelectric article returns to its original shape, and is clamped to the lens barrel. Furthermore, when the voltage turns off, the laminated piezoelectric element returns to its original length. In consequence, the bimorph piezoelectric articles are alternately clamped. Moreover, the laminated piezoelectric article is elongated and restored, and a lens is moved forwards and backwards.
Moreover, it is described in Patent Document 3 that the piezoelectric element is brought close to a rotary feed member for feeding the lens holding unit, and this piezoelectric element rotates the rotary feed member in a stepping manner. Here, the piezoelectric element is brought into contact with a circumference of an end portion of a feed screw for driving the lens frame.
Furthermore, it is described in Patent Document 4 that two types of piezoelectric elements are integrally attached to a guide member which guides the lens holding unit, and these piezoelectric elements alternately perform an expanding and contracting operation to allow the guide member to perform an intermittent feed operation. Here, the piezoelectric element is disposed on the end portion of the feed screw for driving the lens holding unit.
Moreover, it is described in Patent Document 5 that an electrical-mechanical energy conversion element (a piezoelectric element) vibrated by applying an electrical signal is brought into contact with an output member having a screw portion, and a movable member is allowed to abut on the screw portion of the output member to thereby rotate this output member by vibration of the conversion element. In consequence, when the screw portion rotates, the movable member is moved in an axial direction of the output member. Here, the piezoelectric element is disposed around a cylindrical portion of the feed screw end portion.
In addition, it is described in Patent Document 6 that a sleeve portion integrated with the lens barrel is slidably fitted into a guide bar. Moreover, a vibrator of a linear driving type vibration wave actuator is brought into contact under pressure with the outer peripheral surface of a sleeve portion via a leaf spring, and two alternating voltages having a predetermined phase difference are applied to the piezoelectric element to thereby apply a thrust to the sleeve portion in the axial direction, and the lens barrel is moved along the optical axis.
Moreover, with respect to one movable lens frame, each ceramic vibrator is disposed on either the movable lens frame or a fixing portion (the lens barrel) of a lens device, the ceramic vibrator is brought into contact under pressure with a part of either the movable lens frame or the fixing portion on which any ceramic vibrator is not disposed, and the lens is driven by an elliptic motion of the ceramic vibrator.
Furthermore, as shown in FIG. 36, a lens holding unit 1 is engaged with a screw portion 3 of a driving shaft 2 disposed rotatably around an axis, a vibrator 4 including a piezoelectric element is allowed to abut on a peripheral surface of the driving shaft 2, and the driving shaft 2 is rotated by the vibration of the vibrator 4 to move the lens holding unit 1 forwards and backwards along an axial direction of the driving shaft 2.
In addition, as shown in FIG. 37, a piezoelectric vibrator 5 is pressed onto a guide member 8 by a leaf spring 6, the piezoelectric vibrator 5 is stored in a sleeve section of a movable lens holding member 7, a transmission member for converting a rotating motion of a motor into a linear motion is eliminated to improve a space efficiency, and a lens driving device is miniaturized.
It is to be noted that as the driving source using the piezo element, for example, in Patent Document 7, a driving source is described which includes at least one rectangular piezoelectric plate having a long edge portion, a short edge portion and first and second surfaces. Electrodes are attached to the first and second surfaces. Moreover, a ceramic spacer is attached to the center of a first edge portion of the edge portions, an elastic force is applied to the center of a second edge portion opposite to the first edge portion to press the ceramic spacer onto an object, and either of an alternating voltage and an asymmetric single polarity pulse voltage is applied to the electrodes.
Moreover, similarly as the driving source using the piezo element, in Patent Document 8, a driving source is disclosed which includes a first piezoelectric plate having first and second long sides, first and second short sides, front and back surfaces surrounded with the long and short sides, a plurality of electrodes connected to this front surface and a counter electrode connected to the back surface; and a second piezoelectric plate having first and second long sides, first and second short sides, front and back surfaces surrounded with the long and short sides, a plurality of electrodes connected to the front surface and a counter electrode connected to the back surface. A first spacer is attached to the first long side at one end in the vicinity of the first short side of the first piezoelectric plate, and engaged with the surface of the object. A second spacer is attached to the first long side at one end in the vicinity of the first short side of the second piezoelectric plate, and engaged with the surface of the object to press the spacers onto the surface of the object. The first short side of the first piezoelectric plate is disposed substantially in parallel with and close to the first short side of the second piezoelectric plate so as to apply exciting voltages to the plurality of electrodes.
Furthermore, similarly as the driving source using the piezo element, in Patent Document 9, a driving source is disclosed which includes a piezoelectric plate having two long edge portions, two short edge portions and a spacer attached to one of the long edge portions; and at least one arm constituted to be rotatable around the axial center. The arm is provided with first and second end portions disposed at opposite ends of the arm which are distant from the axial center; a read/write head attached to the first end portion of the arm; and a rigid member disposed on the second end portion. The spacer of the piezoelectric plate is elastically urged toward the rigid member so that the piezoelectric plate is movable with respect to the axial center.
Similarly as the driving source using the piezo element, in Patent Document 10, a driving source is disclosed in which a plurality of electrodes are arranged on one surface of a piezoelectric plate, a counter electrode is disposed on the other surface, a head is disposed at one end of an arm rotatable around an axis, a rigid member is, disposed at the other end of the arm, and the piezoelectric plate is elastically urged toward the rigid member.
Furthermore, similarly as the driving source using the piezo element, in Patent Document 11, a driving source is disclosed in which the piezo element causes a motion in a first direction, when a voltage is applied between a first electrode group and a common electrode. A motion is caused in a second direction, when a voltage is applied between a second electrode group and the common electrode. A switch connects the first and second electrode groups to a constant voltage to selectively cause the motion in the first or second direction.
In addition, similarly as the driving source using the piezo element, in Patent Document 12, a driving source is disclosed in which a vibrator has a rectangular parallelepiped shape formed of a plurality of thin layers constituted of a piezoelectric material. This layer includes first and second comparatively large square main surfaces which are identical to each other. Each main surface is defined by a long end surface and a short end surface, layers are laminated, the main surfaces are bonded to each other so that electrodes are present on the surfaces of the layers, and a contact region is disposed on one or more end surfaces of the layers. In consequence, a voltage is applied to each electrode in order to excite a vibration in the contact region.
Patent Document 1: Japanese Patent Application Laid-Open No. 7-63970;
Patent Document 2: Japanese Patent Application Laid-Open No. 5-107440;
Patent Document 3: Japanese Patent Application Laid-Open No. 4-212913;
Patent Document 4: Japanese Patent Application. Laid-Open No. 4-212910;
Patent Document 5: Japanese Patent Application Laid-Open No. 8-47273;
Patent Document 6: Japanese Patent Application Laid-Open No. 7-104166;
Patent Document 7: Japanese Patent Application Laid-Open No. 7-184382;
Patent Document 8: Japanese Patent No. 2980541;
Patent Document 9: Japanese Patent Application Laid-Open No. 9-37575;
Patent Document 10: Japanese Patent Application Laid-Open No. 2000-40313;
Patent Document 11: Japanese Patent Publication No. 2002-529037; and
Patent Document 12: Japanese Patent Publication No. 2003-501988.